Update version, changelog, release notes for 1.2.0-preview5

[alerickson]

PR Summary

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• PR has a meaningful title
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• Summarized changes
• Make sure all .h, .cpp, .cs, .ps1 and .psm1 files have the correct copyright header
• This PR is ready to merge and is not Work in Progress.
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• Breaking changes
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  • Documentation needed
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• User-facing changes
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  • Documentation needed
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• Testing - New and feature
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  • Make sure you've added a new test if existing tests do not effectively test the code changed
• Tooling
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[alerickson]

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[alerickson]

/azp run

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